Reciprocating slat floor conveyors are used in van bodies and semi trailers and other cargo containers with open tops for transporting a variety of bulk cargos. The open tops facilitate loading. The vehicles equipped with floor conveyors, transport cargo to cargo receiving areas. The reciprocating floor conveyors unload the cargo in the receiving area. The reciprocating slat floor conveyors work well for unloading bulk cargo such as wood chips saw dust, silage, grain and fodder that has been ground, rolled or formed into pellets for livestock feed. Food products for human consumption are also transported and unloaded. Reciprocating slat floor conveyors are also used for transporting and unloading caustic materials such as sewage sludge and poultry litter.
Reciprocating slat floor conveyor floor slats are usually extruded aluminum members that are generally three to six inches wide and may be over fifty feet long. Each floor slat is supported by and slides on a plurality of molded plastic slide bearings. One bearing that can be used is disclosed in U.S. Pat. No. 7,104,393, the disclosure of which is incorporated herein by reference. The aluminum floor slats work well in most conditions. Aluminum slats also slide well on molded plastic slide bearings. With an adequate sub floor, aluminum floor slats can support pallets with cargo and fork lift trucks employed to load and unload pallets. The rate of wear of aluminum is acceptable if the slats do not make sliding contact with each other. Sliding contact between aluminum members may result in galling and premature slat destruction.
Caustic materials such as sewage sludge and poultry litter reduce the useful life of aluminum floor slats to an unacceptable short time period. To overcome the problem, polyvinyl chloride (PVC) floor slats were developed. PVC does not react with caustic materials such as poultry litter. PVC also eliminates the galling problem. Vertical edge surfaces of two adjacent floor slats can therefore be in sliding contact with each other and thereby create a seal that prevents cargo loss. PVC floor slats are in use today for transporting and conveying caustic cargo. Floor slats made from plastic and fiber reinforcements have also been produced. These slats are generally relatively expensive and add weight.
Cargo contamination is a concern with cargo containers having reciprocating slat floor conveyors. The contamination can be caused by loss of contaminated cargo that is being transported, through worn or damaged conveyor floor slat seals. Any loss of contaminated grain that can spread to and contaminate additional grain fields is to be avoided. Contamination can also be caused by pathogens entering the cargo container through slat seals. Air borne contaminants that can enter or escape from grain in a cargo compartment are of concern because of their ability to be widely spread in the atmosphere by wind.
A fixed solid sub floor conveyor can eliminate the loss of cargo and the contamination of cargo by toxic substances passing through an undamaged container floor. Sub floors have been made from plastic materials as well as metals such as aluminum. Unfortunately, a solid sub floor under the reciprocating floor conveyor increases the cargo container empty weight and decreases the weight of cargo that can be transported under gross weight limit laws. A cargo container that is a few hundred pounds lighter can reduce operating costs and increase income significantly during the working life of a trailer.
The hydraulic systems employed to reciprocate floor slats are required to provide sufficient force to move each set of floor slats under the highest load conditions. Friction loads between floor slats and floor slat support bearings, between each floor slat and adjacent floor slats, between floor slats and cargo, and between cargo and the cargo container walls are all factors that determine the size and weight of hydraulic system components. Safety considerations when employing fluids under pressure also require consideration. Reduction of the hydraulic fluid pressure required to operate a reciprocating floor slat conveyor will reduce the required size and weight of the drive system and increase the weight of the cargo that can be transported at any given time.